the juniper lic are tied to the hardware id of the device. so you can not move the lic from the 2500 to the the DR site. and from what it sounds like you have a cluster only lic for your 2000 so you can not use that box independently without a master lic.
You can cluster all three of them. You can add the 2000 as a seoncary / passive device and change the cluster option to do not sync log. in active passive the user state info is transfered between the primary and all the hosts so depending on your connection between prod and dr this might not be a viable solution.
In your case i would suggest getting another license for the 2000 so that it is a priamry and not just a cluster member.